Going to manifold vacuum works sometimes, depending on the distributor. The vacuum canister sometimes delivers far too much advance to allow the engine to idle properly in many cases when set up that way so people retard the timing to get a good idle and end up with poor cruise or WOT performance. Tuning is the key. If you want to try manifold vacuum, the way I would set it up is this:
First, you'll need a dial back timing light or a mark on the damper at the 33-34 degree mark.
Next, plug the vacuum port on the carb. Then, unplug the vacuum line to the distributor.
Start the engine and bring the rpm up to 3200-3500 rpm. Using the dial back timing light or your 33-34 degree mark, set the distributor to that point. This way you know for sure you have proper timing at higher engine speeds.
Bring the engine back down to idle speed. When you check the timing it should be in the 8-12 degree range depending on your distributor.
Now plug in the manifold vacuum to the distributor. The advance will probably jump 10 to 12 degrees, maybe more depending on the canister. The idle speed will also increase. Do not move the distributor yet.
Now reset the idle speed. This would be a good time to adjust the mixture. Check the advance. At idle the timing light should be showing as much as 20-22 degrees of advance. If the engine is idling happy, you're good. If not, you need to try to adjust the vacuum canister.
Don't retard the timing to try to get a good idle with the manifold vacuum attached. If you do, what happens is, as soon as you tip into the throttle, your advance retards too far and the engine bogs. Also, at WOT at higher speeds you won't have as much advance as you need.
Your cranking advance should still be the 8-10 degrees you observed without vacuum, but if the starter is struggling, you can retard a couple of degrees to ease that, but be aware that you lose the equivalent at higher speeds.
